Process of rapidly drying timber and other moisture-bearing substances.



1 1). TIEMANN. PROCESS OF RAPIDLY DRYING TIMBER AND OTHER MOISTURE BEARING SUBSTANCES.

APPLICATION FILED JULY 1, 1909.

942, 1 50, Patented Dec. 7, 1909.

alto (mu avwewtoz UNI ED STATES PnTEN ioF IoE,

HARRY n. 'IIEMANN, or NEW HAVEN, CONNECTICUT.

rnocnss or BAPIDLY DRYING mnnnfimn OTHER morsTnnn-rnanme sunsTimcns.

Specification ofietters Patent.

Patented Dec- 7,1909.

Application and m 1 1909. Serial No. 505,454.

nnnrcnan To "THE PUBLIC.

To all whom it may concern; f

Be itknown that I, HARRY D. TIEMANN,

a citizen of the United States, and an employee of the Forest Service, Department of Agriculture,a le 'al resident of the State of Connecticut, resi ing at New Haven, county of New Haven, Connecticut, (whose postoflice address is Yale Forest 3011001,) have invented new and useful Improvements in the Process of Rapidly Drying Timber and other l\-'Ioisture-Bearing Substances, and have .made application by petition of even 'date herewith, under the act of March 3, 1883, chapter 143, 22 Stat, 625, praying that Letters Itatenttherefor may be granted to me.

The invention herein described and claimed may be. used by the Government of the "United States or. any'of its oflicers or employees in the prosecution of work for the United States or by any person in the United States without thereon.

The following is a specification of the said invention: A v

The invention relates to an improvement in the art of rapid artificial drying of wood presence of, carbon dioxid (C0,), or \othernonoxidizing gas or gases, mixed with a certain amount of water vapor, which amount should at first be as much. as the space can contain, and asthe wood becomes drier it should be'approximately proportional to the degree of moisture in the wood, as hereafter explained, and when the-wood has become thoroughly. heated through to the center, cooling' t in-the same gas-from which the water vapor has been removed by condensation, and finally in repeating this operation until the desired degree ,0 'dryness has been reached. This whole operation' may be conducted at atmospheric pres,-

sure, thus doing'away. with the expense of heavy apparatus, or at 'h1gher pressure payment ofany royalty- This is repeated untilrequiring a pressure cylinder, To conduct these operations, the wood is placed in a suitable chamber with non-conducting walls and approximately air-ti ht. It should be i so piled as to allow' of gas between and around each piece. "The Wood maybe run into the chamber on trucks. The gas, previously heated is then passed into this chamber through distributing plates or pipes, so that it Wlll beuniformly distributed and not impinge directly onto ee circulation of the wood, and the exhaust openings should i be. similarly arranged. .lVheu thee-air has been displaced, the exhaust gasmay be reheatedand used over again, thus forming a complete circuit. A certain amount of water vapor is mixed with the heated gas before it enters the chamber, in order to prevent evaporation from the wood during the heating process; If the wood is very wet this: will be unnecessary since enough vapor will be supplied by the water in the wood to partially saturate the gas. .In partially dry wood, however, the gas should be partially saturated with vapor to a degree aniroximatel corresponding to the degree oi'dryness o the-wood. It should not be enough to cause condensation on the wood. The temperature of the wood itself, which vat first wil be less than that oft-he surrounding gas, is determined by means of a recordin pyrometer, with aflexible bulb, the recor ingdial being outside of the chamber, and

the bulb placed. in contact with the wood. When the wood has .remained'in this condition long enough to become uniformly heat-- ed clear through to the center (requ-1rmgabout'an hour for partially dry wood one inch thick, or half an hour for wet Wood, and longer times-according to the thickness), the entering gas isthen cooled and atthe same time thew'ater vapor removed.. there- ,fromby condensation, thus a circulation of cold, dry gas is' maintained in laceof the hot moist gas, until the wood cooled throughout. -When heated under pressure eater than atmospheric, the ressure sho'u d be reduced dunng'the cooling.

as become The efiect of this is that the moisture in the wood is evaporated by the,heat of the wood itself. 'When the-wood has -cooled,.the eration is again (gone through with, using less vapor mixe with the heating gas;

' thedesired degree present with the gas should correspondapproximately to the degree of mo sture in the wood.

The duration of each process depends upon the species of'wood, it s'moisture condition, its dimensions and degree to which it is heated, and the pressure of the gas used. Each operation may require from less than one hour to several hours. If conducted underpressure less time is required. In the absence of air or moisture wood may be heated to a much higher temperature without injury, than when either air or moisture is present. ,In fact a temperature may be used which would totally destroy the wood for useful purposes if in contact with air or moisture. For example, spruce may be safely heated to 170 C. or even higher under these circumstances. 3

The principles upon which these operations are based may be briefly described as follows:

. (1) The wood is heated bymeans of the circulating gas and not by radiation from the walls or from heating coils. Thus the inner parts ofthe stack of wood are heated .as Well as the outer part, resulting in the most uniform heating which it is possible to obtain. The greater the pressure of the gas, the'more rapid the heating.

Evaporation during the heating process is prevented by means of the amount of water vapor mixed with the gas. This is a vital point, since evaporation during heating of a piece of wood must necessarily be most rapid at the surface, where it receives the heat, thus causing case hardening and unequal shrinkage; With, a very wet piece of wood, this does not apply at first, since considerable evaporation of the freewater may take place before any shrinkage begins, and the danger of checking does not occur until the-wood begins to shrink. Shrinkage begins in most 'woods' when at a moisture content of from 25 to 30 per cent.

. of the dry weight.

(3) By cooling-the wood in gas free from w ter. vapor or 1n a vacuum, evaporation so tak esplace and is caused by the heat con- 'tained within the wood itself. As the .amount evaporated is proportional to the loss in temperature, it follows that the tendency is for evaporation to take place from the interiorof the block as much as from the's'urface, for as soon as evaporation be-' gins at the surface, that portion is cooled and the action checked, whereas it continues from the warmer interior portion of, the

block. The action is thus self regulating, and the result is as near a uniform evapo- "ration throughout the block clear to the eenter asnit is possible to "obtain. It is the uhequaldiying which causes internal strains ,ings E and E.

dueto unequal shrinkage and these internal strains cause checking, honey combin warping and other harmful effects. Whi c it may be impossible to avoid all internal strains absolutely, this process of drying by uniform evaporation throughout the block, reduces them to a minimum. Case-hardening is prevented by this method, if rightly conducted.

(4) Treating the wood in the absence of oxygen overcomes oxidation at high temperatures.

(5) When the wood has cooled to the temperatureof the surrounding gas, evaporation practically ceases, and the tota l. amount. of water -which has evaporated depends upon the temperature to which the wood was heated. In practice it is economy of time not to wait until the wood has completely cooled to the lower temperature.

'(tl) In order to remove the remaining moisture, the entire operation is again gone. through with, and this is repeated until the desired degree of dryness is attained. The wood can be rendered absolutely dry by this means, but in most cases a. reduction to 3 or 4 per cent. of the dry weight is all that is do sirable. Ordinary air dried wood contains about 12 per cent. of moisture.

As the wood becomes drier the temperature to which the wood is raised may be inand sequence of treatments are Drying wood more rapidly .without injury than has heretofore been possible. (2)- The productv -.is rendered less hygroseopicby the high temperatiires, when again exposed to the outside air. That is to say, its moisture content is less and changes less with changes of humidity of the air, than is the case of air-dried wood. The strength is. in-- creasedon account. of the reduction in moisture. l) VVarping,-working, shrinking and swelling are reduced, for the same reason. (5) The resonant. quality so much desired in musical instruments is increased.

It isto be understood that while speaking of wood in the above description, the process is applicable to other moisture-bearing substances, and I deslre my Letters Patent to cover the use of this method for drying all such materials.

The accompanying. drawing re resents a.

running the length of the'kiln and separated from the interior by the distributing grat- The shaded portions represent impermeable walls of-concrete or other such material. The exit flue, O, is at either end of the air space just beneath the root.

through the grating, E, to the roof, where it passes'ithrough the flue O; thence down through the condensing coil, and back into the fan X. The as is dried to the desired degree, or humidi ed 'to the proper amount, according to the temperatures of the eon-. (lensing coil,T, and the Water bath of the humidifier, H, respectively. The degree of heat in the kiln, Q, is controlled by. the heating f coilfN, and the temperature of the wood recorded by the autographic thermometer, D,

the bulb, D, lumber.

Non-oxidizing gas is supplied through of which is placed among the pipe R on the entering side of the fan X.

a F are rollers.

Tight canvas and sliding wood or metal doors'are used at the ends of the kiln.

A and-B are pipethermometers; and

'Iclaim: f .r 1. In the process of drying wood and other? moisture-bearing substances, animprovement conslstmg 1n the comblnatlon' and sequence of the following operations:

' presence of or by means of the same or other heating the substance by means of a nonoxidizing'gas or gases mixed with a certain amount of watervapor until the substance is uniformly or nearly uniformly heated throughout, then followed by cooling in they gas or gases containing less water. vapor and repeating this same said sequence ofoperations until the desired effect and degree of dryness'are obtained.

2. In'the process/of drying wood and other moisture-bearingsubstances, an im-v and sequence of the following operations: heating the substance by means of a nonoxidizing gas or gases at or near atmospheric pressure mixed. with 'a certain thoroughly heated through, then followed by cooling at or nearatmo'spheric cpressure by. means of or in the presence of the same or other gas or gases containing less water vapor, and repeating this same said sequence of operations until the desired effect and degree of dryness are obtained;

other moisture-bearing substances, an improvement cons1st1ng 1n the combination and sequence of the-followlhg operations;-

oxidizing gas or gases mixed with a certain amount of water vapor at pressure greater than atmospheric until the substance is thoroughly heated through, then followed by cooling at reduced pressure by means of or in the presence of the same or other gas I or gases' 'containing .less water vapor, and

repeating this same said sequence of-operatlons until the desired effect and degree of dryness are obtained. 1

. t. In the process ofdrying wood and other moisture-bearing substances, an imand sequence of the following operations:

oxidizing gas or gases'mixed with a certain amount of water vapor until the substance 1s uniformly or nearly uniformly throughout, then followed by cooling 1n the presence of or by means of the same or other gas or gases containin less water vapor, and repeating this sai sequence of operations \and increasing the temperature: to which the substance is heated as the substance approaches dryness, until the desired effect and degree. of d ness is obtained. 1

t HAR Y D. TIEMANN.

.Witnesses:

H. E. MCKENZIE, W. D. BRUsH.

provement consisting in" the combination- 3. In' the process of drying wood and heated 1 amount of water vapor, until the substance heatingthe substance by means of a nonprovement consisting in the combination heating the substance by 'means of a none 

